Research Reports

Development of High Performance Concrete and Evaluation of Construction Joints in Concrete Floating Bridges

Description:

Floating bridge concrete must be watertight, durable, workable, and must have sufficient cohesiveness to prevent segregation in heavily congested deep walls. The mix design must experience minimal creep and shrinkage to reduce prestress losses, and cracking. As a result of recent concrete research, new mixes were created incorporating various quantities of fly ash, silica fume, metakaolin, poly-carboxylate ether superplasticizers, and Caltite waterproofing admixture. This research focuses on concrete with a water binder ratio of 0.33 and a slump in the range of 8 to 9 inches. Workability characteristics of the fresh concrete are analyzed and hardened concrete properties tested in this research are compressive strength, chloride ion permeability, and creep and drying shrinkage properties.

It was found that metakaolin was successful in producing mix designs with similar properties as Silica fume modified concrete. Satisfactory strength was achieved through increasing the fly ash and lowering the silica fume contents, though, chloride ion permeability was negatively affected. The removal of silica fume and the inclusion of Caltite decreased the concrete’s resistance to chloride ion permeability and produced concrete that failed to attain the required 28-day ultimate compressive strength of 6500 psi.

The second part of this study focuses on developing an experimental setup to evaluate products and construction methods to help prevent water leakage through construction joints in pontoon floating bridges. A pressure system was used to apply significant pressures to concrete test specimens containing a construction joint. Different products and construction methods were used in constructing the joints to determine the most effective methods for preventing water penetration in the field.

The testing results have shown compaction effort is the most important factor in water leakage through a joint. Increased compaction in laboratory specimens leads to less water leakage through construction joints. Product selection was ineffective in preventing water leakage if concrete compaction was inadequate.